This invention broadly relates to internal coating materials for a cathode ray tube which are characterized by the fact that, in order to increase the electric resistivity of the internal coating, synthetic zeolite powder (which is a form of sodium aluminosilicate) with the primary particle size of 0.5 to 20 microns, and more preferably 1 to 7 microns, is used together with electrically conductive graphite powder.
The invention also relates to internal coating materials in which the zeolite powder has been processed, mainly by heating at a temperature of 150.degree. to 1000.degree. C., to remove excess water before incorporation in the coating composition, and more preferably said temperature is from 400.degree. to 1000.degree. C.
This invention also relates to internal coating materials in which all or a part of the sodium ions are substituted with other alkaline and/or alkali earth metal ions.
This invention also relates to internal coating materials in which the pigment ratio of silicate particles to graphite is variable to such an extent that the specific electric resistance of a coating baked at 430.degree. C. could be within the range of 0.05 to 34,000 .OMEGA..cm. Preferably the electric resistance is within the range of about 0.1 to 3000, and most preferably within the range of about 1 to 300 .OMEGA..cm.
This invention also relates to internal coating materials in which a portion of the zeolite is replaced by one or more nonconductive materials such as iron oxide, titanium oxide, chromium oxide, aluminum oxide, silicon oxide and silicon carbide.